Beyond the answers - interesting background to this quiz

A river that refuses to stay in one place

The Columbia begins in the Canadian Rockies and flows through just two US states, Washington and Oregon, before emptying into the Pacific. For much of its course it forms the border between them. It is one of the great rivers of North America, and its basin drains parts of several other states and British Columbia.

The many faces of a Russian empress

Catherine II, born a German princess, came to Russia to marry the future Peter III and ended up ruling in her own right from 1762 until 1796. Her reign saw territorial expansion, legal reform and a flowering of the arts. The title "the Great" was given to her by later generations, not by herself.

Wagner and the opera that took decades

Richard Wagner spent roughly twenty-six years composing the four operas that make up The Ring of the Nibelung, finishing the cycle in 1874. The complete work was first staged at Bayreuth in 1876, in a theatre built specifically for it. It remains one of the most ambitious projects in the history of music.

When hydrogen burns, the result is surprisingly simple

Burning hydrogen in oxygen produces water and releases energy. This clean reaction is why hydrogen is discussed as a possible fuel: its only combustion product is water vapour, with no carbon dioxide. The same principle powers hydrogen fuel cells, which generate electricity rather than heat.